Plants accumulate storage products in seeds, tubers and tuberous roots. Commonly known storage products include storage proteins, storage starches and storage oils. These storage products, along with serving as sources of nutrition for young plants until they become capable of autotrophic growth by means of photosynthesis, are also an important source of nutrition for animals—including man, and also serve as industrial starting materials. Such storage products generally are accumulated only at specific periods and in specific tissue associated with maturation of the plant. However, were one to have the ability to control the storage product accumulating functions of a plant, it may then be possible to modify the accumulation of storage products in terms of period, place, or quantitatively and qualitatively, and thus obtain such storage products at will. Various investigations are being conducted on the accumulation of storage products in plants towards this very end.
For example, three proteins, ABI3, FUS3 and LEC2 having the plant-specific B3 DNA-binding domain, are known to be transcriptional control factors which regulate the maturation program that includes the accumulation of storage proteins and oils in the seeds of mouse-ear cress (Arabidopsis thaliana). These proteins have been reported to regulate the seed maturation program together with the transcription factor LEC1 and the plant hormone abscisic acid (Int J Dev Biol 56, 645-651 (2005)). Elsewhere, the inventors have identified HSI2, HSI2-L1 (also referred to below as “HSL1”) and HSI2-L2 (also referred to below as “HSL2”), which are similarly B3 DNA domain-binding proteins, as transcriptional control factors associated with sugar responsive gene expression control, and conducted analyses on these factors (Plant Physiol 138, 675-685 (2005); Plant Biotech 22, 371-377 (2005)). It is known that these transcriptional control factors all have the B3 DNA-binding domain, and that a sequence similar to the transcriptional repression motif EAR is present on the C-terminal side thereof.
In addition, an attempt to increase the oil content of seeds by genetic manipulation (Japanese Patent Application Laid-open No. H9-313059) and the accumulation of oils in root tips as a result of mutations (Science 277, 91-94 (1997)) have been disclosed.